One of the motives for taking a photographic portrait is based on uncertainty and insecurity. Since we desire to dismiss loss and lacking, we are eager to locate the self in a flawless photograph as if we can achieve wholeness. This assimilation relates to the theory of "Mirror Stage"  by the French psychoanalyst Jacques-Marie Emile Lacan (1901-1981). The theory suggested that we construct the concept of 'I' through identification with the other. As we believe the other is complete, we assimilate the selves into the flawless photograph to achieve wholeness. Indeed, this alienation is only an image. We misrecognise it as the real self by the assumption from the other people. "We love being seen as the satisfaction of the desire of the other."  Our desire is the desire of being desired. We desire to be the desire of the other. Photographic self-portrait accomplishes us as seeing and as being seen; as photographing and as being photographed; as desiring and as being desired.
On the other hand, we believe we can find our authentic selves. But indeed, it is impossible to have an authentic self. The construction of our identities is actually restricted by the dominant symbolic order. We construct our identities by the presupposed standards, as well as the influences and burdens from history. Owing to these limitations, we realise the necessary freedom of choice. These provoke the anxiety of our existence; we are in doubt of the meanings of our surroundings. We believe if we assimilate the self into the others, then we can dismiss our anxieties of insecurity and uncertainty. However, locating the self in a photographic portrait can never satisfy us because the image is never an authentic self. Therefore, taking a photographic self-portrait is, hence, an endless desire.
Wai Kit Lam
 Lacan, Jacques, Ecrits: a selection; trans. Fink, Bruce in collaboration with Fink, Heloise and Grigg, Russell (New York, 2002), pp.3-9.
 Brown, Michael, Why the Photographer Does not See: Lacan, the objet Petit a and the Gaze in Antonioni's Blow-up, http://www.lacan.org.brown.htm